CASE #1: SCD surgery - left middle fossa craniotomy and canal plugging
IMPORTANT: Surgical plugging of SCD is only indicated IF a patient has intolerable dizziness and vertigo associated with the ear that also has aural (ear) fullness and autophony. This surgery should NOT be performed if a patient only has hearing loss (air-bone gap or supranormal bone conduction) or aural fullness or autophony alone.
LEFT MIDDLE FOSSA CRANIOTOMY - this is a surgical approach through the side of the skull, above the left ear. A hole, about 2 inches square, is made in the skull, the dura (lining) of the brain is gently retracted off of the skull base, the SCD is identified, and the defect is either plugged or resurfaced. Plugging is associated with a more stable repair but potentially with a higher risk of mild to moderate hearing loss.
Although resurfacing has not yet been shown to be associated with hearing loss, there is a higher incidence of recurrence of dizziness.
The other advantage to a middle fossa craniotomy is the exposure that is obtained during the surgery. Often, the skull base surround the SCD is also very thin, or even dehiscent (like Swiss-cheese) - and requires a repair using a thin slab of bone harvested from the same bone flap that is raised during the initial craniotomy. This ensures that the entire skull base is repaired, not just the SCD. Why is this important? Holes in the skull base can lead to other problems, like a small portion of the brain (with the lining called the dura) to push through and fill the middle ear or mastoid. This is called a meningoencephalocele.
Most patients following a middle fossa craniotomy are able to return home following a 1-2 day hospital stay.
Above: Three-dimensional CT scan reconstruction of the skull showing the relative location of a left-sided middle fossa craniotomy. This craniotomy is centered above the external auditory canal to gain sufficient exposure of the middle fossa skull base floor and the arcuate eminence of the left superior semicircular canal.
This 27 year old woman with SCDS presented with left sided aural fullness, autophony, hearing loss, and chronic dizziness and vertigo that worsened with heavy lifting, exertion, and loud noises. Hearing testing showed a mixed left-sided hearing loss and her VEMP testing showed low thresholds and large amplitudes in the left ear. Temporal bone CT scans reformatted to Poschel and Stenver projections revealed a left-sided superior canal dehiscence.
A left-sided middle fossa craniotomy is performed, centered over the external auditory canal.
Once the dura covering the temporal lobe of the brain is exposed, it is retracted to expose the skull base of the middle fossa
A dehiscent skull base (tegmen) is seen.
Gentle, extradural dissection is continued to expose the skull base
As the arcuate eminence (the bony prominence where the superior canal is found above the level of the skull base) is exposed, copious irrigation around the membraneous labyrinth (the internal membrane of the superior canal that is seen when the bone is uncoverd) is used to minimize injury to the inner ear.
Once the SCD is fully exposed, bone wax is gently pressed into the defect, plugging both limbs of the dehiscent canal.
A multilayer reconstruction using bone graft, fascia, and Hydroset cement is used.
Titanium miniplates are used to secure the bone flap.